1. Field of the Invention
This invention relates to a numerical control system capable of correcting the position of an object, or more in particular to a numerical control system which, examining all the time the position of a work table or other object without any absolute position detector, produces a correction or alarm signal in the case of a deviation from a standard or reference position.
2. Description of the Prior Art
Conventional numerical control systems without any absolute position detector, such as a feed-back system using pulse counts and an open loop system driven by a pulse motor have the following disadvantages:
(1) When the power supply is cut off, the current position of a work table or other object of a machine tool or industrial machine to be controlled is missed, and therefore it is necessary to reset the reference position after the power supply is restored. For this purpose, a reference position is required to be set at a point on the control axis and an origin must be restored in order to enable reactuation from that particular reference position. PA1 (2) In the case where the machine fails to follow command pulses due to a mechanical trouble or electrical malfunction, errors in the position of a working table or like object accumulate. If these errors are to be detected during the machine operation, a special device is required. Since this is usually difficult, it is common practice to identify the degree of errors by examining the precision of a work piece involved.